The present invention relates to a reinforced composite vessel and, more particularly, to a vessel of improved design and an improved method for its manufacture.
Filament winding long has been used to manufacture reinforced composite vessels. A general review of the state of the art may be found in W. D. Humphrey and S. T. Peters, "Filament Winding", Concise Encyclopedia of Composite Materials (Kelly Anthony, editor), Pergamon Press, 1994, pp. 368-377, which is incorporated by reference for all purposes as if fully set forth herein. Briefly, one or more strands composed of many filaments of a material such as fiberglass are impregnated with a liquid resin binder and wrapped around a mandrel, and the wrapped mandrel is cured to polymerize the binder. Typically, a cylindrical mandrel is rotated about its axis and a strand delivery system is translated parallel to the mandrel axis to produce a helical wrapping pattern. Most often, one strand, or a band of several adjacent strands, is used to wrap a mandrel supported externally at two ends, as illustrated in FIG. 1 of Humphrey and Peters. Known variations of the process include:
1. Wrapping the mandrel with one or more dry strands, followed by coating the wrapped mandrel with the liquid resin binder. See, for example, U.S. Pat. No. 3,210,228, to Bluck.
2. Simultaneously wrapping the mandrel with several strands delivered from a plurality of ports disposed circumferentially around the mandrel, as taught for example in U.S. Pat. No. 3,255,976, to Mede, and in European Patent Application 0 370 109, both of which are incorporated by reference for all purposes as if fully set forth herein.
Conventionally, the mandrel is supported horizontally and externally at both ends. A notable exception is the above-referenced U.S. Pat. No. 3,255,976, which describes the wrapping of a vertical mandrel, supported from below, to produce a rocket motor casing.
The term "strand" is used herein as in U.S. Pat. No. 3,282,757, to Brussee, to denote individual filaments, of any shape, as well as rovings, flat bands, ribbons and the like which may be made up either as integral members or of a plurality of filaments. The material laid down on the mandrel in one translational pass of the mandrel past the strand delivery system is denoted herein a "stroke".
Several aspects of the filament winding process are susceptible to improvement. When several strands are used to wrap the mandrel, it is necessary to interrupt the winding process at the end of each stroke, to anchor the strands to the mandrel. The dry-wrapping process has several advantages: the resin binder of inner strokes does not begin to cure while the outer strokes are being applied; and the strands can be impregnated in a restricted space with less waste of excess binder and fewer emissions of solvent vapors; but if the resin is applied to dry strands after the winding process has been completed, care must be taken to ensure that the resin does not include dissolved gases that could produce voids in the cured resin, and to ensure that the resin coats all the strands uniformly. Because relatively small amounts of catalyst are used to polymerize the resin, care also must be taken to make sure that the catalyst is mixed uniformly with the resin.
Another problem endemic to prior art reinforced composite vessels is the phenomenon of "basket weave". This is described by D. T. Jones, I. A. Jones and V. Middleton in "Improving composite lay-up for non-spherical filament-wound pressure vessels", Composites: Part A, Vol. 27A pp. 311-317, which article is incorporated by reference for all purposes as if fully set forth herein, as "where successive fibres overlap each other and a laminate structure is formed containing large voids since discrete areas are not covered". Jones, Jones and Middleton propose a single roving winding strategy that reduces basket weave.
There is thus a widely recognized need for, and it would be highly advantageous to have, an improved filament winding process for manufacturing a reinforced composite vessel.